According to Earth system scientists at the University of California, Irvine, the Pacific Ocean's overturning circulation "flipped" during the last ice age, changing the location of ancient waters rich in carbon dioxide.
The researchers argued in a paper published in Science Advances that this change in the 3D churning of such a large ocean basin must have increased CO2 sequestration in the deep sea, lowering the amount of the greenhouse gas in the ice-age Earth's atmosphere.
They discovered this transposition by analyzing carbon-14, or radiocarbon, traces in thousands of fossil sediment samples from around the world, some dating back 25,000 years.
Scientists uncover ice-age shift in Pacific Ocean circulation
JOSEPH PREZIOSO/AFP via Getty Images
It's intuitive to think that the Pacific would have played a significant role in climate regulation during the last glacial period-huge, it's twice the volume of the Atlantic-but scientists didn't have a lot of data to back that up previously, according to lead author Patrick Rafter, an Earth system science assistant researcher at UCI, as per Phys.org.
After compiling and analyzing the data from our study, they can now confidently state that changing overturning circulation in the Pacific is consistent with the ocean being a significant driver of lower greenhouse gases during the last ice age.
Carbon-14, Rafter said, is the isotope of choice for researchers hoping to reconstruct the deep sea-atmosphere relationship over long time scales.
"Radiocarbon is produced in the atmosphere when cosmic ray neutrons collide with nitrogen, and it turns into carbon dioxide after chemical reactions with oxygen, and it then enters the ocean exactly like regular CO2, because it is CO2," Rafter explained.
It's because of this that carbon-14 is such a powerful and useful tracer of how the ocean interacts with the atmosphere.
He and his colleagues used techniques perfected over decades in UCI's Department of Earth System Science for this project, as well as cutting-edge machinery custom-designed to perform this type of carbon dating.
Professors Ellen Druffel and Sue Trumbore, the department's founding faculty members, were determined to make UCI a world-leading center for the use of carbon-14 in geosciences research beginning in the 1990s.
Obtaining funding for what would eventually become the W.M. Keck Carbon Cycle Accelerator Mass Spectrometer Facility, as well as the appointment of John Southon, a UCI Earth system science researcher, to oversee lab operations.
The team collected marine fossils from all over the world, sand grain-sized bits that were identified by more than 20 Earth system science undergraduates working in Rafter's Croul Hall laboratory space with a bank of microscopes.
The calcium carbonate shells were then transformed into graphite, a pure form of carbon.
This material was fed into the Earth system science department's accelerator mass spectrometer, which produced precise radiocarbon measurements-values equal to the seawater in which the fossils lived.
Rafter described the next step as "a bit like assembling a puzzle in which we had to combine our research with previous studies."
There had previously been working done on the North Atlantic, which made sense because it is an important region where the ocean breathes in the atmosphere and where a large amount of carbon dioxide enters the ocean.
Rafter added their own analysis of fossil radiocarbon from sediment cores in the Pacific and Southern oceans, allowing us to interpret all of the major ocean basins for the past 25,000 years for the first time.
According to Rafter, this new knowledge about the deep sea's relationship with the atmosphere dating back to the last ice age can help oceanographers and Earth system scientists fully comprehend the role of the ocean.
Global temperatures were significantly colder than they are today for the majority of the last million years.
Ice encroached closer to the equator, sea level fell, and wind patterns changed, as per Oceans at MIT.
Ice was more than one km thick at the last glacial maximum, some 20 thousand years ago, where Chicago, Stockholm, and Glasgow now stand, indicating that the global climate was radically different from what it is today.
Paleorecords indicated that ocean circulation was less stable during the last ice age than it has been in the last 10,000 years.
Changes in ocean circulation patterns may have caused or contributed to dramatic changes in high-latitude temperatures, sea ice cover, and precipitation patterns.
Increased CO2 storage in the ocean during ice ages is due to a combination of factors, including global ocean cooling, changes in ocean circulation and sea ice coverage in the Southern Ocean, and an increased supply of iron from windblown dust, resulting in more complete nutrient consumption in the Southern Ocean and a stronger 'biological pump' moving carbon into the deep sea.
It is critical that we have a better understanding of the past behavior of these mechanisms in order to analyze the impact of future changes on carbon storage in the deep sea, as well as the viability of carbon sequestration schemes involving the ocean.
